The invention pertains to a process for the recycling of spent indium oxide-tin oxide sputtering targets (ITO targets) and of compacted material residues left over from the production of such targets. The process is applicable particularly in the case of partially reduced targets.
Oxide ceramic targets of indium-tin oxide (ITO) are used for the production of thin, transparent, electrically conductive layers by sputtering. Such layers are used especially in flat-screen technology. The thin indium oxide-tin oxide layers can be produced either by the sputtering of metal targets in a reactive oxygen atmosphere or by the sputtering of oxide ceramic targets.
The sputtering process with oxide ceramic targets offers the advantage that, because of the minimal flow of oxygen in the sputtering chamber, it is easier to regulate the sputtering process than it is when metal targets are sputtered, which requires high oxygen flow rates.
With respect to solid oxide targets of In.sub.2 O.sub.3 +SnO.sub.2, targets which have a substoichiometric oxygen content offer the advantage that the oxygen content crucial to the conductivity of the layer can be adjusted over a wider range while the layer is being sputtered on. In addition, the working range, that is, the range of optimum layer conductivity as a function of the oxygen flux, is wider with these partially reduced targets than it is with solid oxide targets.
The production of these partially reduced targets is quite complicated and expensive. Suitable processes are described, for example, in U.S. Pat. Nos. 4,690,745 and 4,962,071, and in DE-OS 44 07 774 to which U.S. Pat. No. 5,480,532 corresponds.
A significant portion of the target cost is attributable to the high price of the raw material indium oxide. Depending on the sputtering cathode used, spent sputtering targets still contain 60-80% of their original weight. These spent targets would therefore still be quite valuable if it were possible to reuse them again as a raw material.
A solution to this problem already implemented in practice consists in dissolving the spent targets in an acid solution (e.g., as InCl.sub.3) and to return this solution to the very beginning of the material cycle, i.e., before the step in which the powder is produced. Because all the steps of powder production must be carried out again, this is a very time-consuming and expensive process. In addition, it is necessary to work with corrosive or toxic chemicals, which often presents a problem to the target manufacturer. Another disadvantage of this process is that, because of the associated system technology, operations can be carried out economically only when very large amounts of material are available, and all of the know-how of powder production is required.